Sewage treatment by activated sludge in combination with alpha preliminary tank treatment



Jan. 29, 1929. 1,700,722

K. IMHOFF SEWAGE TREATMENT BY TIVATED SLUDGE IN COMBINATION WITH A P LIMINARY TANK TREATMENT Filed Aug. 25, 1924 Mfr/6.3565: I I 77/8/7/01': W an; W

Patented J an. 29, 1929.. v

UNITED STATES PATENT OFFICE.

KARL IMHOFE, OF ESSEN, GERMANY.

SEWAGE TREATMENT BY ACTIVATED SLUDGE IN- COMBINATION WITH NARY TANK TREATMENT.

A PRELIMI- Application filed August 25, 1924, Serial-No. 734,011, and in Germany July 15, 1924.

The hitherto known methods of sewage treatment by activated sludge work mostly without preliminary tanks, because the crude sewage can be purified in the aeration tanks practically as'well as sewage pre-treated in settling basins. The preliminary tank treat ment is, however, of very great importance in the treatment of the sludge itself. The better the pre-cleaning, the smaller is the quantity of excess sludge afterwards produced in the aeration tanks and the lower are the costs required for a disposal of said excess sludge which can only be treated with difliculty.

In the accompanying drawing: Figs. 1 and 2 are respectively a sectional front elevation and a plan View of a diagrammatical arrangement, in which a combined settling and digestion tank is provided for a preliminary treatment of the sewage.

The digested sludge is dried on the drying beds 70. The discharge from the settling basin (1 flows through the aeration tank I). At the bottom of the latter compressed air is sup- I plied in a way known in the art, which aerates the activated sludge therein and raises the same in a rising pipe 00 so. that it cannot settle at the bottom. The discharge from the aeration tank I; flows through the hopper bottom tank 0 which separates the activated sludge from the then purified discharge. To always have the necessary quantity of activated, sludge in the aeration tank I), the sludge eliminated in the hopper bottom tank 0 is continuously raised by means of compressed air in a rising pipe 2 therein and led through a pipe d into the supply conduit e of the aeration tank 6, coming from the basin (1. This portion of the activated sludge is named: return sludge.

Thecompressed' air required for aerating the activated sludge in the aeration tank 6 and for raising the sludge from the hopper bottom tank 0 is produced in the engine house f and supplied through pipes g to its places of destination.

Beside the return sludge, of which the quantity is always constant, on each working day a certain quantity of excess sludge is produced in the plant, which cannot be used in the aeration tank I) and must he removed.

For this purpose, said excess sludge is led from the hopper bottom tank 0 through a pipe h to the crude sewage supplyconduit of the preliminary tank or basin a. Thereby,

the following advantages are attained: (1)

The activated sludge has a high adsorptive" power and sinks very quickly. By mixing it with the incoming crude sewage, it adsorbs a large portion of the very fine suspended matters therein, which otherwise do not settle in the settling basin, and sinks to the bottom with the same; thereby improving the settling action of the settling basin or preliminar tank a. (2) A special treatment of the sludge by reason of its high amount of moisture becomes unnecessary, this being of greatest importance. However the preliminary treatment of thesludge may be, it is always an advantage to dispose of the activated sludge together with the sludge of the preliminary tank. This applies particularly to the digestion of the sludge in digestion tanks. Wherever it has been attempted to let the activated sludge decompose alone, it was found that a very long time and very large chambers are required for this purpose. The decomposition becomes more favorable by adding to the activated sludge digested sludge from the digestion tanks of the preliminary treatment. most simple way by the method above pro- This is attained in a posed, that is by leading the excess sludge into the supply conduit of the preliminary tank. If, for instance, a combined settling and digestion tank a (Fig. 1) .is provided for the preliminary treatment of the crudesewage, the different sludge particles when settling from the sewage arrive together at the digestion tank and are there at once exposed to methane fermentation. The excess acti-f vated sludge disappears in the digestion tanks almost completely, because it consists practically of water only and of organic matters which are gasified durin the digestion. Thus, the preliminary tanks need not bemuch larger than in conventional plants,

and the quantity of methane gained is inliminary or' settling tank, conducting the sewage .next to an aeration tank, and then through a sedimentation and separation tank, and returning activated sludge from the sedimntation tank to the preliminary settling tank and the aeration tank.

3. The method of sewage treatment by activated sludge in passing'thesewage successively through a preliminary or settling tank, an activation and. aerationtank and a separation and sedimentation tank which consists inactivating the sewage and the sludge and introducing air into the activated sludge aeration tank; separating and sedimenting the sludge in the separating tank; returning a part of the separated activated sludge. from the separation tank into the aeration tanks; and returning another. part of the separated activated sludge from'the separation tank into the preliminary tank.

I 4. 'A plant for carrying through sewage treatment by activated sludge, comprising in combination a preliminary tank adapted for carrying through a preliminary settling "of the sewage and digesting of the sludge;

an intermediate tank adapted for carrying through the inoculation and the activation of the sewage and the sludge; a tank adapted them in the before mentioned order; means for activating and for aerating the sludge in the intermediate or aerating tank; means for returning the so called return activated sludge from the separation tank into the aeration tank; and means for returning the so called excess activated sludge from the separation tank into settling and digesting tank, 40

,In testimony whereof I have hereunto 'set my hand.

KARL IMHOFF. 

